docs: def center(self, axis=1):
          """
          Subtract the mean either within or across records.
  
          Parameters
          ----------
          axis : int, optional, default = 1
              Which axis to center along, within (1) or across (0) records.
          """
          if axis == 1:
              return self.map(lambda x: x - mean(x))
          elif axis == 0:
              meanval = self.mean().toarray()
              return self.map(lambda x: x - meanval)
          else:
              raise Exception('Axis must be 0 or 1')